Applications brief: AFM-IR spectroscopy and imaging of polymers fibers and thin films at the nanoscale

Key points


  • AFM-IR captures the correlation between structure, processing, and chain orientation/crystallinity in electrospun nanofibers and thin films
  • Determines how different processing protocols can alter the concentration of the stable alpha and metastable beta crystalline forms
  • Evaluates crystalline populations as a function of nanofiber diameter and as a function of the location within the fiber
  • For the first time, the existence of a core-shell structure as a function of location within the nanofiber have been observed
  • Ability to produce a map of the secondary structure of crystalline structure as a function of location within the nanofiber

Key words

AFM-IR | polymers | nanofibers | thin films

Authors

John Rabolt, Liang Gong, Bruce Chase, Isao Noda, Curtis Marcott

Abstract

The combination of atomic force microscopy (AFM) and infrared (IR) spectroscopy is an extremely powerful tool that can provide topographic information that can be correlated with chemical, conformational and molecular orientation information at a spatial resolution of 50-100 nm.

Using an AFM-IR instrument, we have explored the correlation between structure, processing and chain orientation/crystallinity in biodegradable and biocompatible poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) electrospun nanofibers and thin films and tested the hypothesis that different processing protocols can alter the concentration of the stable α-crystalline form and the metastable ß-crystalline form.

The ability to obtain IR spectra at high spatial resolutions has allowed us to probe, for example, crystalline populations as a function of nanofiber diameter and as a function of location within the fiber and we have observed, for the first time, the existence of a core-shell structure in a single electrospun nanofiber. In addition, the spectroscopic imaging capability of the AFM-IR instrument has been utilized to create a map of α and ß crystalline content as a function of location within the nanofiber and this clearly verifies the existence of a core-shell structure.

AFM-IR used on single electrospun PHBHx fibers collected on (a) aluminum foil (473nm) and (b) the tapered edge of a rotary disk (324nm). (c) IR spectra of fibers for the AFM images (a) and (b). The red dots on the fibers specifies the position of the AFM tip

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